Carbonaceous refractory shaped body with improved oxidation behavior and batch composition and method for producing the same

ABSTRACT

A batch, in particular for the production of a refractory shaped body, includes at least one refractory metal oxide component and a synthetic resin component as a binder, and a graphitizing auxiliary for producing crystalline graphite carbon from the resin. The graphitizing auxiliary originates from a group consisting of reducible organic compounds of transition elements and/or a group of active organic or inorganic metal compounds or metals, such as resin-soluble metal salts, chemically precipitated or micronized metal oxides or metals. The graphitizing auxiliary is available in molecular form over the time and/or temperature range of conversion of the synthetic resin into carbon (carbonization).

BACKGROUND OF THE INVENTION

The invention relates to a refractory batch for the production of ashaped body and to a process for its production.

Phenolic resin-bonded or pitch-bonded bricks based on magnesia and otheroxides as well as graphite are preferably used to line metallurgicalvessels. Very high demands are imposed on the performance of the bricksat application temperatures of up to 1800° C. with aggressive, movingslags.

The wear to refractory bricks in use can be roughly divided into twodifferent mechanisms: firstly, the wear caused by chemical reactions(corrosion and oxidation), and secondly thermomechanical wear (cracks,flaking, fatigue of the brick substance). There are also mixed forms,such as abrasion and erosion. While the chemical stability can beinfluenced in particular by the choice of raw materials (LC sinter,fused magnesia, flake graphite, etc.), the thermomechanical resistanceis determined above all by the bonding. In use, MgO-C bricks inprinciple have four possible ways of compensating for thermomechanicalloads; by elastic deformation, by plastic deformation, by microcracks orby macrocracks in the brick structure. While the elastic component ofthe deformation is naturally low in coarse ceramic products, macrocrackslead to destruction and loss of brick substance.

Under the high application temperatures in the metallurgical vessels,the binders phenolic resin and coal-tar pitch are carbonized to formcarbon. The binder is therefore only a means to an end. However, thenature of the resulting carbon, which is responsible for bonding in thebricks under the high application temperatures, is determined by thebinder. The nature of phenolic resin bonding means that it has thedrawback, compared to pitch bonding, that the carbon which is formedduring carbonization (glassy carbon) is rigid and brittle. Pitch-bondedbricks, with high strengths, have relatively low moduli of elasticity.The primary difference is the crystallinity of the carbon, which inpitch results from the formation of a liquid so-called mesophase.Corresponding structures are produced from the phenolic resin understandard conditions only at temperatures of over 2500° C. Unlikecrystalline graphite, glassy carbon bonding in practice offers no way ofcompensating for excess stresses apart from by macrocracks. The resultin practice is a higher sensitivity to thermomechanical stresses andmechanical impact loads. Moreover, the isotropic glassy carbon reactsmore readily with oxygen, i.e. is more sensitive to oxidation. In use,this may lead to a more rapid loss of brick substance.

The pitch bonding, which is based on coal-tar pitch, however, has theconsiderable drawback that, when the pitch and the bricks are heated,carcinogenic substances, such as benzo(a)pyrene, may form, and thesesubstances have to be removed from the brick immediately after they havebeen produced using complex heat treatment methods. Therefore, pitchbonding is under pressure with regard to health and safety at work andenvironmental protection. The use of newly developed, alternativepitches originating from petroleum generally leads to a reduction in theperformance of the bricks. Therefore, there is a need for bonding withoptimum use properties, in particular a high flexibility and resistanceto oxidation of the bonding coke, in combination with environmentallycompatible emissions during production and use.

It is known from “Chemical Abstracts”, Vol. 109, No. 20, Nov. 14, 1988,Abstract No. 1753313e, to add 3-20% by weight of metallic aluminum oraluminum alloy powder and 0.5-7% by weight of chromium oxide powder toresin-bonded magnesia-carbon bricks. This is intended to improve theresistance to oxidation/corrosion.

To accelerate and control the liquid-phase pyrolysis of industrialhydrocarbon mixtures, in particular bonding pitches for refractoryshaped bodies, it is known from DE 43 12 396 A1 to add, for example,ferrocene in order to increase the yield of coke. This allows the cokeyield to be catalytically increased.

BRIEF SUMMARY OF THE INVENTION

The invention is based on the object of providing a refractory batch anda refractory shaped body which is thermoplastically deformable and,moreover, has an improved oxidation behavior, the positive useproperties of the phenolic resin bonding being linked to the goodthermomechanical properties and the higher resistance to oxidation ofthe coal-tar pitch bonding.

The object is achieved by a batch having the features set forth below, ashaped body also having the features set forth below, and also a processwhich has the features set forth below.

According to the invention, the objects are achieved by the fact thatthe graphitization of the synthetic resin which is carbonized isachieved by the addition of graphitizing auxiliaries to the binder resinat temperatures of even <1000° C.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is also explained by way of example by reference to adrawing, in which:

FIG. 1 shows the lines from X-ray diffractograms for carbonized resolresin, pitch and resol resin which has been mixed with a graphitizingauxiliary in accordance with the invention;

FIG. 2 shows softening under load/compressive flow (SUL/CF) curves underargon;

FIG. 3 shows the resistance to oxidation of a shaped body according tothe invention compared to known shaped bodies.

DETAILED DESCRIPTION OF THE INVENTION

The graphitizing auxiliaries according to the invention are inparticular readily reducible organic compounds of the transitionelements, such as for example metallocenes, metal benzoates, metaloctoates and metal naphthenates, or active, optionally inorganiccompounds, such as resin-soluble metal salts or chemically precipitatedor micronized metal oxides. Preferred metals in this context are Cu, Cr,Fe, Ni or Co. However, metallic graphitizing auxiliaries, such as theabovementioned metals and in particular Ni metal or further metals suchas Pt metal, Rh metal, Ge metal or similar or other related metals, arealso conceivable. The substances which are active as graphitizingauxiliaries reduce the graphitizing temperatures of 2500° C. which areotherwise customary to below 1000° C., and are added in amounts from 0.1to 10% by weight, based on the resin. A typical amount is 1%.

The agent is for example dissolved in solvent or added in micronizedform as a powder or slurry. The crucial factor is that the elementswhich act as graphitizing auxiliaries are available in molecular form atthe start of the conversion of the synthetic resin into carbon(carbonization) at approx. 400-500° C. This requires an extremely fine,ideally molecular dispersion of the active substance and alsoreducibility under the conditions in the MgO-C brick. The graphitizingaction can no longer be measured at below 0.1%. The agent is dissolvedin solvent or is added in micronized form as a powder or slurry.

The graphitization of the synthetic resin can be determined in purecarbonized synthetic resin specimens by X-ray diffraction.Non-graphitized carbon provides only a diffuse, broad peak, whilegraphitized synthetic resin has the characteristic diffraction spectrumof graphite. The graphitizing auxiliary in the binder matrix of thebrick is detected, for example, by EDX scanning of the binder matrix ofa microscopic brick specimen on the catalytically active element (e.g.Fe, Ni or Co).

FIG. 1 shows the lines from X-ray diffractograms for carbonized resolresin, pitch and resol resin which has been mixed with a graphitizingauxiliary in accordance with the invention. The sharp peak at 25° showsthat the catalytic activation leads to crystalline, graphite structures.The carbonized resol resin only reveals what is known as an amorphoushill, indicating a low state of order.

FIG. 2 shows softening under load/compressive flow (SUL/CF) curves underargon. During the testing of the SUL, the test specimen, which issubjected to a constant load, is heated to the testing temperature andthe change in length is measured. The specimen generally grows, onaccount of thermal expansion. The higher the thermal expansion, thehigher the stresses in the brick. In the case of compressive flow,pressure and temperature are kept constant and the deformation ismeasured as a function of time. If the material has an ability to flow,it is deformed in the opposite direction to the expansion, althoughfurther growth, for example on account of reactions taking place and newphases being formed, is also conceivable.

The bonding according to the invention using a graphitized carbonizedsynthetic resin was produced by adding 1% of ferrocene dissolved inacetone to the novolak resin. The diagram shows that the invention notonly leads to lower expansion than standard synthetic resin bonding butalso leads to a pronounced ability of the brick to flow. The profile ofthe curve makes it possible to draw the conclusion that, on account ofthe lower expansion, stresses not only occur to a reduced extent, butalso can be relieved without destruction. The modification thereforeleads to a thermoplastic behavior of the refractory shaped body, withoutthe other properties dropping to a level which is below that of brickswith standard resin bonding.

This is also demonstrated by the following table, which compares theproperties of bricks with and without bonding which has been graphitizedby means of graphitizing auxiliaries (statistical means from theproduction of approx. 500 t of bricks). Two batches were selected andbricks produced therefrom.

-   Batch 1: 90% fused magnesia 96, 10% C-   Batch 2: 90% fused magnesia 96, 10% C, addition of 1% of micronized    ferrocene powder to the batch.

Batch 1 Batch 2 FRD [g/cm³] 3.06 3.06 FRD a.c. [g/cm³] 2.97 3.00 Emodulus [GPa] 48.81 56.88 E modulus a.c. [GPa] 9.20 7.73 Open porosity[%] 4.37 3.23 Open porosity a.c. [%] 11.25 10.13 Cold compressionstrength 51.60 58.30 [MPa] Cold compression strength 20.10 23.10 a.c.[MPa] Cold flexural strength [MPa] 13.18 15.15 Cold flexural strength2.48 2.87 a.c. [MPa] d max [%] 1550° C. 1.88 1.58 Ability to flow after10 h 0.31 0.45 [%] 1550° C. d max [%] 1300° C. 1.53 1.46 Ability to flowafter 10 h 0.00 0.05 [%] 1300° C. Resistance to oxidation 19.15 22.13[s/mg] a.c. = after carbonization

In particular the high strengths and low open porisities in combinationwith the low elastic moduli (E modulus and G modulus) after theformation of the graphite carbon structure at 1000° C. are worthy ofnote. Furthermore, the formation of a crystalline, graphite structure ofthe carbon considerably improves the resistance to oxidation, measuredas burnoff per unit time under a defined air flow at 1000° C.(thermogravimetry), as shown by FIG. 3.

The invention is to be explained in more detail with reference to twoexamples.

1. Shaped Body with Ferrocene as Graphitizing Auxiliary

First of all, a micronized MgO-ferrocene preparation is produced bymilling an MgO sinter with a grain size of 1-2 mm and ferrocene powdertogether in a ball mill, in a ratio of 50:1. After the milling, thefinal grain size of the ferrocene lies in the range of 1-10 μm and istherefore highly active. The milling takes place in order to open up theferrocene and allow handling which is easier for metering to the batch.

Further raw materials used are fused magnesia and flake graphite. Thebatch consists of 34% of fused magnesia of a grain size of 2-4 mm, 22%of fused magnesia of a grain size of 1-2 mm, 20% of fused magnesia of agrain size of 0-1 mm and 12.5% of MgO meal. In addition, the batchincludes 10% of flake graphite and 1.5% of MgO-ferrocene preparation.The batch described above is fed to a forced mixer, where it issubjected to dry premixing for three minutes. Then, 3% of phenolic resinare added and mixing is continued for a further 10 minutes. The pressbatch produced in this way is pressed to form shaped bodies on ahydraulic press under a maximum pressure of 160 MPa. The shaped bodiesare then dried for six hours at 200° C., after which they are ready foruse.

2. Shaped Body with Fe Pigment as Graphitizing Auxiliary

In this case, Fe pigment is used as graphitizing auxiliary, the Fepigment which acts as graphitizing auxiliary (red hematite pigment,grain size <10 μm) being added directly to the resin, as a slip with asolid content of >60%. This pigment suspension is stirred into the resinby means of a stirrer. Homogenization is achieved after approx. fiveminutes and can be recognized from the fact that the pitch is coloredall the way through.

Further raw materials used are once again fused magnesia and flakegraphite, with a batch being produced from 34% of fused magnesia with agrain size of 2-4 mm, 22% of fused magnesia with a grain size of 1-2 mm,20% of fused magnesia with a grain size of 0-1 mm and 14% of MgO meal.10% of flake graphite are added. These constituents undergo drypremixing for three minutes in a forced mixer. Then, 3% of phenolicresin, of which 1.5% is dispersed Fe pigment suspension, are added tothe mixer, whereupon the entire mix undergoes wet-mixing for a further10 minutes.

This press batch, which is now fully mixed, is likewise pressed intoshaped bodies on hydraulic presses using a maximum pressure of 160 MPa,these shaped bodies being dried for six hours at 200° C. after pressingand then being ready for use.

Of course, the ferrocene may also be processed as a suspension and Fepigment may also be processed as an MgO-Fe pigment preparation. Allfurther graphitizing auxiliaries which have been mentioned and arepossible can likewise be processed at least in the two ways which havebeen described. Moreover, they can be added to the resin or the entiremixture or other individual constituents of the mixture, in the form ofa suspension or emulsion in a very wide range of solvents.

An advantage of the of the carbon-containing refractory batch and shapedbody according to the invention is that bonding in the batch or shapedbody which allows a high degree of flexibility and resistance tooxidation on the part of the bonding carbon is achieved, while avoidingthe environmental problems associated with pitch, while the graphitizingtemperature is advantageously reduced from over 2000° C. to well below1000° C.

1. A batch, for production of a refractory shaped body, comprising: atleast one refractory metal oxide component; at least one carbon carrierand a synthetic resin component as a binder; a graphitizing auxiliaryfor producing crystalline graphite carbon from the synthetic resincomponent; the graphitizing auxiliary originating selected from thegroup consisting of reducible organic compounds of transition elementsand/or a group of active organic or inorganic metal compounds or metals;and the graphitizing auxiliary having a size in molecular form over atime and/or a temperature range of a conversion of the synthetic resininto carbon via carbonization.
 2. The batch as claimed in claim 1,wherein the graphitizing auxiliary contains, as reducible organiccompounds of the transition elements, metallocenes and/or metalbenzoates and/or metal octoates and/or metal naphthenates and/or furtherorganic metal compounds.
 3. The batch as claimed in claim 1, wherein theorganic compounds are compounds of metals, the metals being copperand/or chromium and/or iron and/or nickel and/or cobalt and/or platinumand/or rhodium and/or germanium.
 4. The batch as claimed in claim 1,wherein ferrocene is included as the graphitizing auxiliary.
 5. Thebatch as claimed in claim 1, wherein the graphitizing auxiliary includesinorganic metal compounds, the inorganic metal compounds beingresin-soluble metal salts or chemically precipitated or micronized metaloxides or metals.
 6. The batch as claimed in claim 1, wherein thegraphitizing auxiliary contains, as the inorganic metal compounds,compounds of copper and/or chromium and/or iron and/or nickel and/orcobalt and/or platinum and/or rhodium and/or germanium or contains themetals in metallic form.
 7. The batch as claimed in claim 1, wherein thegraphitizing auxiliary contains red hematite pigment.
 8. The batch asclaimed in claim 1, wherein the refractory metal oxide componentsubstantially includes MgO.
 9. The batch as claimed in claim 8, whereinthe refractory metal oxide component is a high-purity natural orsynthetic MgO sinter.
 10. The batch as claimed in claim 1, wherein therefractory metal oxide component substantially includes dolomite. 11.The batch as claimed in claim 10, wherein the refractory metal oxidecomponent is a natural or synthetic dolomite sinter.
 12. The batch asclaimed in claim 1, wherein the refractory metal oxide component isAl₂O₃.
 13. The batch as claimed in claim 12, wherein the refractorymetal oxide component is tabular alumina.
 14. The batch as claimed inclaim 1, wherein the synthetic resin component includes asingle-component synthetic resin.
 15. The batch as claimed in claim 1,wherein the synthetic resin component includes a two-component syntheticresin.
 16. The batch as claimed in claim 1, which includes antioxidants.17. The batch as claimed in claim 16, wherein the antioxidants aremetallic antioxidants.
 18. The batch as claimed in claim 17, wherein themetallic antioxidants are silicon and/or aluminum and/or magnesium. 19.The batch as claimed in claim 1, wherein the refractory metal oxidecomponent has a grain size less than or equal to 10 mm.
 20. The batch asclaimed in claim 1, wherein the refractory metal oxide component has agrain size distribution less than or equal to 5 mm.
 21. The batch asclaimed in claim 1, wherein the refractory metal oxide component in thebatch is between 70% by mass and 98% by mass.
 22. The batch as claimedin claim 1, wherein the binder is a phenolic resin and/or a resol resinand/or a novalak resin.
 23. The batch as claimed in claim 1, wherein thesynthetic resin component is included in an amount of from 1 to 5% bymass.
 24. The batch as claimed in claim 1, wherein the carbon carrier isincluded in an amount of from 0.5% by mass to 30% by mass.
 25. The batchas claimed in claim 17, wherein the metallic antioxidants are includedin an amount of from 0.5% to 10%.
 26. The batch as claimed in claim 1,wherein the graphitizing auxiliary is included in amounts of from 0.1 to10% by weight, based on the synthetic resin component.
 27. The batch asclaimed in claim 26, wherein the graphitizing auxiliary is included inamounts of from 0.5 to 5% by weight, based on the synthetic resincomponent.
 28. The batch as claimed in claim 26, wherein thegraphitizing auxiliary is included in amounts of from 0.7 to 1.4% byweight, based on the synthetic resin component.
 29. The batch as claimedin claim 1, which includes fibers.
 30. The batch as claimed in claim 29,wherein the fibers are steel fibers.
 31. The batch as claimed in claim1, including means for using the batch for producing shaped bodies. 32.The batch as claimed in claim 1, including means for using the batch asa spraying and/or tamping and/or ramming and/or repair compound.
 33. Aprocess for producing a shaped body using a batch, comprising:classifying and assembling a refractory metal oxide component to have agrain-size range including a plurality of grain fractions; mixing therefractory metal oxide component with a carbon carrier and a syntheticresin component as a binder to form a mixture; adding and mixing agraphitizing auxiliary to the mixture for producing crystalline graphitecarbon from the synthetic resin component in the mixture; and pressingand then hardening the mixture.
 34. The process as claimed in claim 33,wherein antioxidants are also added to the mixture.
 35. The process asclaimed in claim 33, wherein the graphitizing auxiliary is added, as amicronized, premilled preparation including the refractory metal oxidecomponent and the graphitizing auxiliary, the premilled preparationbeing produced by milling the refractory metal oxide component and thegraphitizing auxiliary together in a ball mill.
 36. The process asclaimed in claim 35, wherein, for the premilled preparation, thegraphitizing auxiliary and the refractory metal oxide component aremixed in a ratio of 1:50 and are milled together in the ball mill. 37.The process as claimed in claim 36, wherein milling is continued until afinal grain size of the graphitizing auxiliary is between one and tenmicrometers.
 38. The process as claimed in claim 33, wherein thegraphitizing auxiliary is added to the mixture as a suspension, emulsionor slip.
 39. The process as claimed in claim 33, wherein thegraphitizing auxiliary is added to the synthetic resin component priorto mixing with any other constituent.
 40. The process as claimed inclaim 33, wherein steel fibers and/or pressing auxiliaries are alsoadded.
 41. The process as claimed in claim 33, wherein the batch, whenfully mixed, is pressed at pressing pressures of up to 180 MPa.
 42. Theprocess as claimed in claim 33, wherein the shape bodies, when pressed,are dried and hardened for 4 to 10 hours at 150 to
 250. 43. The batch asclaimed in claim 1, wherein the group consisting of reducible organiccompounds of transition elements includes resin-soluble metal salts;and/or the group of active organic or inorganic metal compounds ormetals includes chemically precipitated or micronized metal oxides ormetals.